This invention relates to improved apparatus for and a method of identifying spectrally pure optical radiation (SPOR) in radiation of unknown spectral purity (RUSP).
The use of radar systems to detect and locate various targets such as aircraft and surface ships is well known. It is desirable and useful in certain situations for personnel in such targets to know when they are illuminated by radar signals and to alarm warning receivers when this occurs. One technique for attempting to achieve this objective in the past has been to use a narrow filter to measure received energy within the bandwidth. A wide spectral signal would have a small fraction of its energy within the filter band compared to a spectrally pure signal. The problem with this technique is that it requires often unavailable prior knowledge of the signal wavelength.
Another prior technique employs an etalon whose spacing is modulated. A spectrally pure signal is indicated by the fringe modulation of the signal intensity detected after the etalon. However, in this technique the spectral function of a pulse signal may not be determined if the unknown pulse rate is not favorable compared to the modulation rate of the etalon.
This invention is directed to apparatus for and a method of determining the presence of SPOR without the foregoing problems and limitations.